oh trussy boyyyy!

I have just got my Spector out of its case for the first time in about 2 months.. I know....
Up above the 12th fret, on some frets the pitch isn't changing, mainly on the G string.
There will be 2 frets next to eachother, and both will ring out the same pitch.
Is this truss rod stuff? I have never touched a truss rod before... getting scared

Before you do anything else, raise the action by raising the height of the g string saddle. At a minimum, this should move any problem with string buzz down to frets lower on the neck. Sometimes the saddle screws slip.
If the problem persists, read the general discussion on setup at the top of this thread.

I just did a check, and the credit card thickness is there.
Yeah it played fine before I threw it in its case, except there has always been a dead fret on the 15th fret A string. No matter how many setups I had, it seemed to just keep buzzing. Now another dead fret has emerged, on the 22nd fret on the G string. The two frets behind it, (20 & 21) are the two frets that ring the same pitch...

You need to take it in to a local luthier and have check all your frets and have them reseat and file them as necessary. When they are completed, all your frets will be the same height and you will no longer have these problems that you described.

Here in San Jose, CA where luthiery prices are high, I paid $125 to have it done to one of my basses.